Bright gold and gold alloy plating baths



l atented Nov. 24, 1953 UNITED STATES TENT OFFICE Barnet l). Gstrow, Brooklyn, N. Y.

No Drawing. Application November 10, 1950,

Seriai No. 195,139

5 Claims. 1

The present invention directed to electrolytic baths, more particularly to baths for the deposition of gold and alloys containing gold.

It has been customary for many years in the plating of gold to utilize bath consisting essentially of gold cyanide together with other substances. If alloys of gold were to be deposited, the bath contained soluble salts of other metals, such as copper. It has been found that in the electrolytic deposition of gold for the purpose of plating various objects, a smooth gold deposit was diillcult to obtain in a single operation. It was also difficult to deposit relatively heavy gold plate so that it was ductile and smooth. In order to overcome these disadvantages, it was proposed to deposit gold on a suitable basis metal in a relatively thin plate and then treat the deposit by a suitable heating cycle and then polishing, hurling or burnishing the deposit. Such a finishing operation was necessary since the deposit was dull and lacked the necessary smoothness, even to the point of being rough.

When heavy deposits were desired, it was nec essary to repeat the cycle two or three times, or in other words, the first deposit was heat treated and buffed, after which a second and a third deposit was made with intermediate and final heat treatment and polishing operations. Such procedure was quite costly in that the article being plated was handled a number of times in various operations. Also, the polishing operation removed gold so that the plate became thin and particularly the removal of the gold deposit was considerable where sharp corners and edges were present. it is at such points that the maximum protection is desired and as a result the protection was not sufiicient to prevent corrosion of the article over extended periods.

In another procedure it had been proposed to provide a bath containing a gold cyanide in a relatively strongly alkaline solution with the addition of glue. Such an addition was intended to give a bright deposit but it was only moderately successful in that a truly bright finish was not obtained. Glue concentrations are critical and the presence thereof caused deposits to become brittle so that flaking of the deposit often occurred with increasing concentrations of glue. Polarisation at the cathode during the operation was increased, introducing difficulties in the operation of the bath.

The present invention is intended and adapted to overcome the diificulties and disadvantages inherent in prior methods of the type described. it being among the objects or the present inven tion to provide an el ctrolytic bath for the deposition of gold and alloys thereof whereby. in a 2 single operation smooth and heavy gold deposits may be obtained.

It is also among the objects of the present invention to provide an electrolytic bath for the deposition of gold alloys thereof, in which the deposits are bright or somi-bright It is further among the objects of the present invention to provide a bath composition which will not interfere with the elastic-deposition or the operation of the process and which will accomplish the desired results.

It is still further among the objects of the present, inventionto provide a bath of the char acter described which will deposit gold and its alloys in such a state that no finishing operations are necessary thereon and particularly avoiding the necessity for burnishing or buifing the surface of the deposit.

In practicing the present invention there is provided a bath of the usual. character containing gold cyanide, usually with other substances such as are commonly used in the art. There is added thereto an organic compound having special properties and particularly imparting to the bath the ability to deposit gold or gold alloys with a bright finish or a semi-bright finish. The degree of brightness may be readily con trolled by alterin'gthe conditions of deposition. The brightness of the deposits obtained by the present invention are e uivalent to the degrees of brightness in the deposition of bright nickel deposits by present day methods. lhe deposits of the present invention have a much greater resistance to corrosion than equivalent thicknesses of gold or? alloys thereof deposited by prior art methods.

The substance added to the bath is one taken from the class of substituted ammoni'as. At least one of the hydrogen atoms of the ammonia is replaced by an organic radical having from 1 to 12 carbon atoms. The organic radical may be merely a hydrocarbon group or the group may have certain substituent radicals thereon. For instance, at least one of hydrogens of the organic radical may be replaced by an amino group or an OH group. While ordinarily the organic radical is or the aliphatic type, are matic radicals may be used. The following are typical of the character of compounds used in the present invention:

Ethylene diamine Diethylene triamine Triethylenetetrarnine Tetraethylenepentamine l-lydroxyethyl ethylene diamine Ainiiioethylethanolamihe The following compounds have also been found suitable for the purpose:

Monoethanolamine Triethanolamine Triisopropanolamine With these compounds the best results are obtained if they are mixed with substances of the first listed group.

Not only the above mentioned substances may be used but others falling within the general class are adapted to give the desired results. It is desirable that the amount of alkali metal cyanide present in the bath be within a definite range depending on the quantity of and the particular alloying metals in the bath (other than gold). In this connection there is used the term theoretical free cyanide. This term is defined as the quantity of alkali metal cyanide above or less than the amount theoretically necessary to form complex cyanide ions with all of the metals present in the bath. It represents that portion of the alkali metal cyanide which in theory is not combined with the metals present to form the complex salts. free cyanide in the bath varies with the s ecitlc amine used, with the operating temperature, and the concentration of metal salts in the solution and may be either positive or negative. It may be desirable to age a fresh bath in order to establish an equilibrium between the various ions in the bath so as to obtain uniform results during the electroplating. The time necessary for aging varies with the temperature and with the particular salts of the alloying metals used in the makeup of the bath; usually, the bath is allowed to stand at room temperature for twentyfour hours. For good adhesion to basis metal, it is desirable to strike in a conventional gold cyanide solution prior to plating in these solutions.

Example 1 The following is an example of a bath made in accordance with the present invention:

Gold metal 1.5 gins. per liter added as gold cyanide (AuCN).

Copper metal 1.0 gm. per liter added as copper sulphate.

Nickel metal 4.0 gms. per liter added as Example 2 The following bath composition has been found suitable for the present purpose:

Gold metal 3.0 gins per liter added as gold cyanide.

Copper metal 2.0 gms. per liter added as copper sulfate.

Nickel metal 8.0 gms. per liter added as nickel sulfate.

Silver metal 0.75 gm. per liter added as silver nitrate.

Diethylenetriamine 35.0 gms. per liter.

Theoretical free KCN +1.5 gins. per liter. Water to make 1 liter. n so to pH=10.5.

The conditions of the operation are approximately the same as those set forth in Example 1. The deposit has the desirable characteristics The amount of the theoretical The pH of the solution noted above and the deposition may be continued to give as heavy a plate as desired. The surface of the finished article is smooth and quite bright and does not require any finishing operations. The protection against corrosion is excellent.

Example 3 Gold (metal) 4.5 gins. per liter added as gold cyanide. Nickel (metal) 12.0 gnls. per liter added as nickel sulphate. Copper (metal) 3.0 gms. per liter added as copper sulphate. Theoretical f-ree KCN -2.0 gms. per liter. Aminoethylethanolamine 30.0 gins per liter. Tetraethylenepentamine 10.0 gins. per liter. H 80 to pH:9.5.

The deposition of the metals takes place under the usual conditions and the temperature may vary from room temperature to about 180 F.

Example 4 Gold (metal) 4.5 gms. per liter added as gold cyanide. Nickel (metal) 0.5 gins. per liter added as nickel sulphate. Theoretlcal free KCN +2.0 gnis. per liter.

Triethylenetetramine 350 gms. per liter.

pH of 3.0 to 11.5 with an optimum of about 9.5-

but the invention will still be operative if these limits are exceeded somewhat.

The amount of amino compound used may be varied and good results have been obtained with from 1 to 100 gms. per liter. Instead of inorganic salts of the metals to be plated, organic compounds may in some cases be used in whole or ill in part. For instance, copper salts of ethylene-- diamine may replace copper sulphate. The fol-- lowing are compounds of this character:

CuEnzl-lzO (Cu(CN) 2) z CuEnz (Cu2(CN) 3) 2 CuEn2Cu3.2I-I2O CuzEnaHzO (Cu (CN) 3 2 wherein En represents ethylenediamine. In the operation of a bath containing copper compounds, gradual reduction to cuprous compounds may occur to such an extent as to interfere in some measure with the brightness of the plate; to avoid this air may be bubbled through the bath at intervals to reoxidize the copper to the cupric form. Or, hydrogen peroxide may be added for this purpose. Alloying metals may be added in the form of compounds which are soluble in the solution, such as metal cyanides, sulphates or chlorides. If, for instance, cuprous cyanide is used, it is preferably oxidized to the cupric state with suitable oxidizing agents.

These and other changes may be made in the details of the invention without departing from the principles herein set forth, and the invention is to be broadly construed and to be limited only by the character of the claims appended hereto.

I claim:

1. An electrolytic bath for plating a metallic material selected from the group consisting of gold and gold-base alloys comprising an aqueous Not only single amino com-- solution of aurous cyanide having therein a sufficient amount of an amine taken from the class consisting of alkyleneand alkylol-amines having 1 to 12 carbon atoms to produce a brighter deposit than is obtained by plating from said bath in the absence of said substance, and containing about 1.5 to 2.0 grams of theoretical free alkali metal cyanide, the pH being from about 8.0 to about 11.5, whereby heavy gold deposits which do not require burnishing are obtainable by electrolytic deposition.

2. An electrolytic bath for plating a metallic material selected from the group consisting of gold and gold-base alloys comprising an aqueous solution of aurous cyanide and a soluble salt of at least one other metal having therein a sufiicient amount of an amine taken from the class consisting of alkyleneand alkylol-amines having 1 to 12 carbon atoms to produce a brighter deposit than is obtained by plating from said bath in the absence of said substance, and containing about 1.5 to 2.0 grams of theoretical free alkali metal cyanide, the pH being from about 8.0 to about 11.5, whereby heavy gold deposits which do not require burnishing are obtainable by electrolytic deposition.

3. An electrolytic bath for plating a metallic material selected from the group consisting of gold and gold-base alloys comprising an aqueous solution of aurous cyanide having therein a surficient amount of an alkylene amine in which the alkylene radical contains 1 to 4 carbon atoms to produce a brighter deposit than is obtained by plating from said bath in the absence of said substance, and containing about 1.5 to 2.0 grams of theoretical free alkali metal cyanide, the pH being from about 8.0 to about 11.5, whereby heavy gold deposits which do not require burnishing are obtainable by electrolytic deposition.

4. An electrolytic bath for plating a metallic material selected from the group consisting of gold and gold-base alloys comprising an aqueous solution of aurous cyanide having therein a sufficient amount of an alkylol amine in which the alkylol radical contains 1 to 4 carbon atoms to produce a brighter deposit than is obtained by plating from said bath in the absence of said substance, and containing about 1.5 to 2.0 grams of theoretical free alkali metal cyanide, the pH being from about 8.0 to about 11.5, whereby heavy gold deposits which do not require burnishing are obtainable by electrolytic deposition.

5. An electrolytic bath for plating a metallic material selected from the group consisting of gold and gold-base alloys comprising an aqueous solution of aurous cyanide having therein a suilicient amount of an amine taken from the class consisting of alkyleneand alkylol-amines having 1 to 12 carbon atoms to produce a brighter deposit than is obtained by plating from said bath in the absence of said substance, said amount being from 1 to 100 grams per liter, and containing about 1.5 to 2.0 grams of theoretical free alkali metal cyanide, the pH being from about 8.0 to about 11.5, whereby heavy gold deposits Which do not require burnishing are obtainable by electrolytic deposition.

BARNET D. OSTROW.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,818,179 Westbrook Aug. 11, 1931 1,991,995 Wise Feb. 19, 1935 2,048,594 Brockman July 21, 1936 2,195,454 Greenspan Apr. 2, 1940 2,355,070 Harford Aug. 8, 1944 2,452,308 Lambros Oct. 26, 1948 OTHER REFERENCES Gilbertson et al.: Transactions of the Electrochemical Society, vol. '79 (1941), pp. 439-42.

Weisberg et al.: Transactions of the Electrochemical Society, vol. (1942), pp. 51012. 

1. AN ELECTROLYTIC BATH FOR PLATING A METALLIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF GOLD AND GOLD-BASE ALLOYS COMPRISING AN AQUEOUS SOLUTION OF AUROUS CYANIDE HAVING THEREIN A SUFFICIENT AMOUNT OF AN AMINE TAKEN FROMTHE CLASS CONSISTING OF ALKYLENE- AND ALKYLOL-AMINES HAVING 1 TO 12 CARBON ATOMS TO PRODUCE A BRIGHTER DEPOSIT THAN IS OBTAINED BY PLATING FROM SAID BATH IN THE ABSENCE OF SAID SUBSTANCE, AND CONTAINING ABOUT 1.5 TO 2.0 GRAMS OF THEORETICAL FREE ALKALI METAL CYANIDE, THE PH BEING FROM ABOUT 8.0 TO ABOUT 11.5, WHEREBY HEAVY GOLD DEPOSITS WHICH DO NOT REQUIRE BURNISHING ARE OBTAINABLE BY ELECTROLYTIC DEPOSITION. 